Ballast circuits are known. As is known, a ballast circuit converts electrical power from a commercially-available source to a form suitable for powering a load-typically one or more discharge lamps. Such ballast circuits typically have electromagnetic interference ("EMI") filters. It is common for such EMI filters to have one or more ground terminals.
A common hazard is the load being coupled to a ground fault condition, thus presenting a path to ground. This may occur, for instance, if a human being makes electrical contact with the load. In this case, current may flow through the human being to ground, thus causing physical injury to the human being. It is known to use a ground fault detector to detect the presence of a ground fault condition and, in response, to disconnect the load from the power source. In the aboveidentified Nilssen patent, for example, the EMI filter acts to produce a control signal in case a ground-fault current were to occur, which control signal is used for preventing the magnitude of the ground-fault current from exceeding acceptable limits. See, Nilssen, col. 2, I. 1-5.
What is disclosed herein is a novel ground fault detector which may be used with any ballast circuit having an EMI filter, wherein the EMI filter includes a ground terminal distinct from the AC power line.